Power tongs or oilfield equipment commonly used to make up and break apart threaded connections on casing, tubing, or other oilfield tubulars. While various types of power tongs have been devised, the type most preferred by many oilfield operators for over fifty years has a tong body or frame with an open throat, and a partial rotary ring or rotary gear with a corresponding throat. When the frame and rotary ring throats are aligned, the power tong may be moved laterally on and off the oilfield tubular. Once the tubular is positioned within the rotary ring, the door attached to the frame is closed and the ring engages the tubular and rotates to make up or break apart the threaded connection.
Because of a need for safety, oilfield equipment operators require guards or doors on the open throat frame of a power tong. If the door is not properly closed before the tong is actuated, an operator hand may accidentally enter the throat area. The high speed rotation of the rotary ring has injured many oilfield operators. In some cases, the worker appendage slips into the area of the rotary ring throat, severely injuring the worker.
Various types of systems have been devised which seek to prevent these injuries, and more particularly allow rotation of the rotary ring only when the tong door is properly closed. When the tong door or guard is opened to allow lateral movement of the power tong onto and off the tubular, the system does not allow rotation of the rotary ring or rotary gear. A common method of accomplishing this goal it utilizes a hydraulic valve adjacent the tong door, with the valve being opened or closed by a pin or other member movably responsive to the door position. The hydraulic valve may be provided with fluid from a line connected to the fluid supply line to the motor, and a return line from the hydraulic valve may be connected to the hydraulic return line from the motor, i.e., the hydraulic tong motor for rotating the rotary ring or gear and the hydraulic valve are fluidly in parallel. When the guard is properly positioned closed, the hydraulic valve is also closed and high pressure fluid is available to power the tong hydraulic motor, thereby rotating the ring. When the door is not properly fully closed, the hydraulic valve is open and bypasses fluid back to the return line. This bypass prevents the buildup of high pressure fluid being supplied to the tong motor, thereby hopefully preventing rotation of the partial ring.
The safety system as described above has several shortcomings which have limited its acceptance, and most importantly have not prevented some accidents to oilfield operators. The prior art system requires additional valves and hoses which must be added to the hydraulic system. These hoses and valves may leak, and in frustration the oilfield operator may bypass this safety system. Moreover, even when the hydraulic valve is opened and fluid is bypassed through the hydraulic valve and returned to the hydraulic power source, some fluid under pressure is still available to drive the power tong motor. Accordingly, the hydraulic valve may be open but the motor may still rotate the ring, although at less than its full speed. Any rotation of the rotary ring or gear with the door not properly closed can be dangerous and may injure the oilfield worker.
In an attempt to overcome the shortcomings of the system described above, another method has been developed for preventing rotation of the rotary ring when the tong door is open. This alternative system completely blocks the flow of fluid to the motor when the hydraulic valve is closed by placing the hydraulic valve and the motor fluidly in series, with the motor downstream from the hydraulic valve. This system has the disadvantage of also requiring additional valves and hoses, thereby making the hydraulic system more complex. As with the system described earlier, the expense of additional valves and hoses and a possibility of fluid leakage encourage the operator to bypass the safety system. Also, this latter system undesirably allows the tong motor to run when the tong door is closed but without an operator intentionally resetting the system. Accordingly, while the tong door should be closed before high pressure fluid to be available to the power tong motor, operator intervention is not required to purposefully initiate or reset the system in order to supply fluid to the power tong motor once the door is closed. If the hydraulic safety valve is accidentally bumped at the same time the motor control valve handle is bumped, the tong motor could restart.
The disadvantages of the prior art are overcome by the present invention, and an improved method and system are hereinafter disclosed for operating a power tong while improving operator safety. The system of the present invention desirably stops rotation of the rotary ring without creeping of the rotary ring in a manner of the system most commonly used in the prior art. Moreover, the system of the present invention does not require altering the conventional fluid delivery system of the tong which supplies fluid pressure from the hydraulic fluid source to the power tong motor.